1. Field of the Invention
This invention relates to a power steering device used as auxiliary means for transmitting a steering force from a steering wheel to tires of a motor vehicle.
2. Prior Art
Heretofore, there have been generally used a recirculating ball type power steering device and a rack and pinion type power steering device.
As the rack and pinion type power steering device, such a construction has been proposed that a pawl provided on a rotatable, axially movable valve spool is engaged with a spiral groove and caused to axially slide along the spiral groove, whereby the valve spool is axially moved to change one oil channel over to the other. However, the abovedescribed device of the prior art has presented such disadvantages that the pawl is fixed onto the spool, and, it cannot be displaced, and therefore, unless the groove surface of the spiral groove is formed with high precision, the pawl cannot slide along the groove surface. On the other hand, if the interval between the groove surface and the pawl is made large to avoid the abovedescribed difficulty in sliding, then the responsiveness of the power steering device is deteriorated for the period of time required for absorbing the excessive clearance resulted from the interval.